After a diagnosis of scabies, how long should it take for the rash-like symptoms to go away? The treatment prescribed was permethrin cream. Is one dose enough or should I continue to use the topical cream until it is gone? Also, my girlfriend does not show any signs of infection. Should she use the cream just in case?

A.C.

Scabies is an infection caused by the mite Sarcoptes scabiei. While it is often thought of as a sexually transmitted disease, it can be spread easily to anyone when there is prolonged skin-to-skin contact or sharing of clothes or bedding, as commonly occurs with sexual partners and household members.

The mite attaches and then burrows itself into the skin, where it lays eggs and defecates. This causes an allergic reaction, resulting in the signs and symptoms of scabies, including severe itching (usually worse at night) and small bumps and tiny blisters on the skin. The presence of linear burrows points to a diagnosis of scabies. The most common sites for the rash include the wrists, the areas between the fingers, and the genitals. In otherwise healthy patients, scabies causes no significant problems, though a bacterial infection can develop in the affected areas. However, in people with weakened immune systems, including those with AIDS, a severe variant known as Norwegian scabies can develop.

The treatment of scabies usually involves a cream. The one most commonly used is a 5 percent permethrin cream (Elimite), which is applied to the entire skin surface, from the chin to the toes, and left on for six to eight hours. Severe cases may require retreatment, but this usually is not necessary. Although an oral drug called ivermectin is very effective in treating scabies, it is infrequently used because it is not FDA-approved for this purpose.

Sexual partners and others who have had close contact with you (your girlfriend, in your case) also should be treated. It can take four to six weeks before symptoms develop after infection, so even though your girlfriend has no symptoms now, without treatment, she may develop the rash later. It can take two to three weeks or longer for all of the itching and rash to completely disappear, though you should not have any new areas of involvement within a day or two after completing the treatment.